1. Field of the Invention
The present invention relates to an in-wheel motor system for use in vehicles having direct-drive wheels as drive wheels.
2. Description of the Prior Art
In recent years, in a vehicle driven by a motor such as an electric car, an in-wheel motor system which incorporates a motor in wheels is being employed due to its high space efficiency and drive force transmission efficiency. The in-wheel motor of the prior art has a structure that a motor portion is fixed to a spindle shaft connected to a part called “upright” or “knuckle” which is a frame dress-up part of the vehicle so that a motor rotor and a wheel can turn. FIG. 72 shows the constitution of an in-wheel motor 80 disclosed by JP-A 9-506236 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”). In this in-wheel motor 80, a rotor 8OR having magnet means (permanent magnet) 80M is installed in a housing 82 fixed to a wheel 81, a stator 80S having a coil 80C is mounted on the inner side of the above magnet means 80M and fixed to a hollow shaft 84 connected to a knuckle 83, and the inner and outer side walls 82a and 82b of the above housing 82 are linked to the above stator 80S by bearings 84a and 84b, respectively, so that the rotor 80R can turn round the stator 80S.
In general, in a vehicle having a suspension mechanism such as a spring around its legs, it is known that as the mass of unsprung parts such as a wheel, knuckle and suspension arm so called “unsprung mass” increases, variations in the ground-contact load of a tire become larger and the road holding properties become worse when the vehicle runs on a rough road.
In the in-wheel motor of the prior art, as the motor portion is fixed to the spindle shaft connected to a part called “upright” or “knuckle” which is a frame dress-up part of the vehicle as described above, the above unsprung mass increases by the mass of the in-wheel motor with the result that variations in the ground-contact force of each tire become larger and the road holding properties become worse.
To solve the above problems, as shown in FIG. 73, there is proposed an in-wheel motor system in which a rotating side case 3b for supporting the rotor 3R of a hollow in-wheel motor 3 and a wheel 2 are interconnected by a flexible coupling 10 comprising a plurality of hollow disk-like plates 11A to 11C and direct-acting guides 12A and 12B mounted to the front and rear sides of the center hollow disk-like plate 11B in such a manner that their moving directions cross each other, and a non-rotating side case 3a for supporting a stator 3S and a knuckle 5 are interconnected by a damping mechanism 90 comprising a damper 92 mounted to a direct-acting guide 91 for guiding in the vertical direction of the vehicle and a spring member 93 which is connected to the damper 92 in parallel and expands and contracts in the moving direction of the above direct-acting guide 91 or a damping mechanism 20K comprising two plates 26 and 27 whose moving directions are limited to the vertical direction of the vehicle by direct-acting guides 21 and which are interconnected by spring elements 22 and a damper 23 moving in the vertical direction of the vehicle as shown in FIG. 74 (for example, see the pamphlet of WO02/83446).
Since the in-wheel motor 3 can be float mounted to the knuckle 5 which is a frame dress-up part of the vehicle due to this constitution, the motor shaft and the wheel shaft can be moved separately in the radial direction. That is, as the mass of the motor is separated from an unsprung mass corresponding portion of the vehicle and serves as the weight of a so-called “dynamic damper”, a dynamic damper effect is added without increasing the unsprung mass. Therefore, variations in the ground-contact load of the tire are greatly reduced and the road holding properties of the vehicle are greatly improved.
However, it cannot be said that the above constitution in which the in-wheel motor 3 is supported by the damper 92 and the spring member 93 which are connected to each other in parallel in the vertical direction is always satisfactory as compared with the constitution of the prior art in which the in-wheel motor 80 is mounted to an unsprung mass corresponding portion because variations in ground-contact load at a frequency near the unsprung resonance frequency are not fully reduced though variations in the ground-contact load of the tire are greatly reduced.
It is an object of the present invention to provide an in-wheel motor system which is excellent in road holding properties by further improving a structure for applying the mass of a motor as the weight of a dynamic damper.